Method and device for manufacturing metallic particulates, and manufactured metallic particulates

ABSTRACT

Produce metal particles offering high purity and uniform granular shape and size: by forming a combustion chamber comprising an injector nozzle for mixture gas of oxygen and hydrogen, an ignition device and a material metal feeder in the upper space of a high-pressure water tank filled with inert gas; igniting inside the combustion chamber via the ignition device the injector nozzle for mixture gas of oxygen and hydrogen and melting (vaporize) the material fed by the material metal feeder; and then causing the produced molten metal droplets to contact high-pressure water and let the resulting metallic particles to precipitate in water.

This application is the U.S. National Phase under 35 U.S.C. §371 ofInternational Application PCT/JP02/02912, filed Mar. 26, 2002, whichclaims priority of Japanese Patent Application No. 2001-91942, filedMar. 28, 2001. The International Application was published under PCTArticle 21(2) in a language other than English.

FIELD OF THE INVENTION

This invention relates to a method and apparatus for producing metallicparticles offering high purity and uniform granular shape and size, aswell as metallic particles produced by the method and apparatus. Theinvention also relates to a production of fine titanium powder, amongothers, as the aforementioned fine metal powder.

BACKGROUND OF THE INVENTION

Raw element metals are processed into various forms, such as moldedshapes, sheet, bar, thin wire or foil, according to applications. Inrecent years the use of metal powder as molding material is drawing theattention in the fields of powder metallurgy, thermal spraying and othermolding techniques. Particularly, powder metallurgy is regarded as animportant technology offering wide applications, including production ofmetal parts, and therefore demand for powder metal—which is the basematerial for powder metallurgy—is also growing.

Production of metal powder traditionally used the classic method ofmechanically and directly crushing metal granules into powder form orthe method to blow molten metal with gas pressure to form powder.However, all these and other methods had difficulty achieving uniformgranular shape and size, economy, and so on.

Electrolysis is one of relatively new methods for metal powderproduction. It has been reported that smooth, minute and uniformcrystalline structures can be deposited under appropriate conditions,and that performing electrolysis outside the range of these conditionsproduces brittle metal of sponge or powder form.

Still, these newer production methods did not produce metal particles ofsatisfactory shape and size uniformity nor did they resolve otherproblems such as economy.

Among other metals, titanium is a relatively new metal compared withiron, copper and aluminum that have been in use since ancient times.Titanium is light and offers excellent strength at high temperature aswell as corrosive resistance, and is therefore used widely in industrialapplications.

The sample applications of titanium include jet engine material andstructural member for aircraft/spaceship, material for heat-exchangersused in thermal and nuclear power generation, catalyst material used inpolymeric chemical products, articles of daily use such as eyeglassframe and golf club head, and material for health equipment, medicalequipment and medical/dental material. The applications of titanium areexpected to grow further. Titanium, which is already competing withstainless steel, duralumin and other high-performance metals in terms ofapplications, is likely to surpass its rivals in the future.

Since titanium metal has poor processability and machinability,producing a mechanical part having complex shape from molten titaniumwill add to manufacturing man-hours and costs. It is because use ofmolten titanium as material will require cutting and other machiningsteps following the plastic working process such as hot forging androlling.

Therefore, powder metallurgy is widely used in titanium metalprocessing, which is the reason for the growing demand for titaniumpowder, particularly one offering high purity and good uniformity ofgranular shape and size. Titanium powder produced by the conventionalpowder production methods designed for general metals is subject to thesame problems with other metals; i.e., irregular granular shape andsize, poor economy, and so on. As a result, development of a productionmethod that can provide titanium powder offering high purity and uniformgranular shape and size is eagerly awaited.

For example, the hydrogenative dewatering method and rotary electrodemethod are being put to practical use as improved production methods fortitanium metal powder. The hydrogenative dewatering method uses spongetitanium, molten titanium or titanium chips generated fromcutting/machining as material. The material titanium is heated in ahydrogen atmosphere to cause it to absorb the hydrogen gas and thusbecome brittle. This brittle titanium is then crushed and heated againin vacuum so that the hydrogen gas will be released and powder formed.In the rotary electrode method, molten titanium or titanium melted thenforged, rolled or otherwise worked is formed into a round bar to be usedas material. This material round bar is turned at high speed in anatmosphere of argon, helium or other inert gas, while its tip is meltedby a heat source such as an arc or plasma-arc torch. The drips of moltenmetal are then scattered via centrifugal force to produce sphericalpowder particles.

The particles of titanium powder obtained by the hydrogenativedewatering method have irregular sphericity. Although this powder can beused in die molding, the heating process must be repeated twice. Acrushing process using a ball mill or other mechanical means may beincorporated, but oxygen contamination of titanium powder cannot beavoided. In the rotary electrode method, material titanium is melted inan inert gas and made into powder form. Therefore, particles arespherical and offer good flowability. They are not subject to oxygencontamination, either. However, the solidification property when moldedwill be reduced. Both methods are a batch system, so the powerproduction cost is high.

The atomization method was developed as a titanium powder productionmethod addressing the aforementioned problems relating to quality andproduction cost. In the atomization method, material titanium is meltedin a water-cooled copper crucible using a plasma-arc torch or other heatsource, in order to cause molten titanium to drip continuously from oneend of the crucible. Argon, helium or other inert gas is then injectedonto the molten titanium to atomize it and obtain powder. However, thismethod could not reduce the production cost significantly from thelevels of the conventional methods, because molten titanium or meltedand worked titanium had to be used as material.

In the meantime, a method for producing powder titanium offeringimproved sphericity and flowability for easier molding, in a mannerrequiring less cost and avoiding oxygen contamination, is disclosed inJapanese Patent Application Laid-open No. 5-93213. In this method,sponge titanium is isostatically pressed cold into a solid bar. This barmaterial is then melted in an inert gas, after which argon, helium orother inert gas is injected onto the dripping molten titanium to atomizeit and obtain powder. However, this improved method did not offer goodpurity or uniformity of granular shape and size and the production costwas not at a satisfactory level, either.

SUMMARY OF THE INVENTION

As described above, there is an increasing need and demand for metalpowder, especially titanium metal powder, with the progress of powdermetallurgy and other new molding methods. However, powder productionmethods that sufficiently answer such demand were not available and theexisting methods had problems, particularly in regard to the purity ofelement metal, uniformity of granular sphericity and size of powder, andproduction cost.

The purpose of the present invention is to provide, in an economicalmanner, element-metal powder material offering excellent uniformity ofgranular sphericity and consistency of granule size, for use in powdermetallurgy and other types of molding, by solving the aforementionedproblems associated with the conventional technologies.

To achieve the above purpose, the inventors conducted various studies toresolve the problems associated with the production of element metalpowder such as titanium powder, including those pertaining to the purityof element metal, uniformity of granular sphericity, consistency ofgranule size and production cost.

With regard to the above, titanium powder can be created during theproduction process for high-function water containing titanium, asspecified in Japanese Patent Application No. 2000-136932 proposedearlier by the inventors.

The aforementioned invention relating to a production of high-functionwater containing titanium (Japanese Patent Application No. 2000-136932),proposed earlier by the inventors, provides a method for producinghigh-function water in which molten titanium is dissolved, wherein themethod is characterized by the burning of a mixture gas of oxygen andhydrogen in high-pressure water and the melting of titanium metal usingthe combustion gas. It was expected that by utilizing this technology,powder offering high purity and uniform granular sphericity and sizewould be obtained and the production cost would also be reducedsignificantly.

However, the aforementioned preceding invention had the problem ofinsufficient melting of material metal, which was caused by a narrowrange of combustion gas atmosphere resulting from a mixture gas ofoxygen and hydrogen being burned in high-pressure water.

After examining various ways, the inventors found that the problem ofthe preceding invention would be solved by burning a mixture gas ofoxygen and hydrogen in a high-pressure water tank having an injectornozzle for supplying a mixture gas of oxygen and hydrogen into its upperspace.

In other words, the present invention, which is based on theaforementioned finding, essentially provides a method for producingmetallic particles, which is characterized by filling the upper space ofa high-pressure water tank with inert gas; forming a combustion chamberin the space comprising an injector nozzle for mixture gas of oxygen andhydrogen, an ignition device and a material metal feeder; ignitinginside the combustion chamber via the ignition device the mixture gas ofoxygen and hydrogen injected from the aforementioned injector nozzle;using the combustion gas to melt (vaporize) the material metal fed bythe material metal feeder; and then causing the produced molten metaldroplets (vapor) to contact high-pressure water to instantly crush andsolidify the droplets/vapor and allow the produced fine particles toprecipitate in water for recovery.

Additionally, the present invention essentially provides an apparatusfor producing metallic particles, which forms a combustion chambercomprising an injection nozzle for mixture gas of oxygen and hydrogen,an ignition device and a material metal feeder, in the upper space of ahigh-pressure water tank filled with inert gas, and consists of apressure-resistant container comprising a pump that feeds the gas in theupper space into high-pressure water and a dryer that dries theaforementioned gas traveling upward in high-pressure water, after thegas is collected and before it is released into the upper space.

The method proposed by the present invention generates virtually nobyproducts or impurities other than the target element metal powder.Occurrence of metal oxidation due to heating of material metal is alsovery small, and since the obtained metal powder has excellent uniformityof granular sphericity and consistency of granule size, the productioncost can be reduced significantly. The method also allows for continuousproduction in addition to batch production, which opens a door tomass-production of metal powder.

In the aforementioned production process, a mixture gas of oxygen andhydrogen is burned in the upper space of the high-pressure water tank toachieve a high-temperature state. This heat is used to melt or vaporizematerial element metal (a metal whose evaporating temperature is equalto or below the combustion temperature of the mixture gas of oxygen andhydrogen will evaporate and become gas). Upon contact with high-pressurewater, the molten droplets or vapor will instantly disperse in water andturn into fine particles to form metal powder.

Unlike the preceding invention (Japanese Patent Application No.2000-136932), the upper space in the high-pressure water tank is filledwith inert gas (such as argon and neon). Therefore, even with achemically active metal such as titanium or zirconium, the molten metaldroplets or vapor produced by the combustion of mixture gas willvirtually remain intact, except for slight formation of oxidized film onthe surface, and will quickly precipitate at the bottom of water inpowder form. As a result, high-purity titanium or zirconium powder willbe obtained.

To sum up, the basic structure of the present invention is to burn amixture gas of oxygen and hydrogen in the upper space of a high-pressurewater tank and use the combustion gas to melt (vaporize) materialelement metal and let it disperse/precipitate in water, therebyproducing metal powder. A schematic drawing of the production process isshown in the production flow chart given in FIG. 1.

The present invention comprises components (1) through (7) below, whichbasically serve to bum a mixture gas of oxygen and hydrogen in the upperspace of a high-pressure water tank and use the combustion gas to melt(vaporize) material metal and let it disperse/precipitate in water,thereby producing metal powder.

(1) A method for producing metallic particles, which is characterized byfilling the upper space of a high-pressure water tank with inert gas;forming a combustion chamber in the space comprising an injector nozzlefor mixture gas of oxygen and hydrogen, an ignition device and amaterial metal feeder; igniting inside the combustion chamber via theignition device the mixture gas of oxygen and hydrogen injected from theaforementioned injector nozzle; using the combustion gas to melt(vaporize) the material metal fed by the material metal feeder; and thencausing the produced molten metal droplets (vapor) to contacthigh-pressure water to instantly crush and solidify the droplets/vaporand allow the produced fine particles to precipitate in water forrecovery.

(2) A method for producing metallic particles as described in (1) above,wherein the gas in the upper space of the high-pressure water tank isfed into high-pressure water via a pump and the aforementioned gas iscollected as it travels upward in high-pressure water, dried and thenreleased into the upper space.

(3) A method for producing metallic particles as described in (1) or (2)above, wherein the material metal is titanium, zirconium, germanium,tin, gold, platinum or silver.

(4) A method for producing metallic particles as described in (1), (2)or (3) above, wherein the shape of the material metal is bar, sheet,wire, foil or granule, or any combination thereof.

(5) An apparatus for producing metallic particles, which comprises apressure-resistant container comprising a combustion chamber comprisingan injection nozzle for mixture gas of oxygen and hydrogen, an ignitiondevice and a material metal feeder, in an upper space of a high-pressurewater tank filled with inert gas, a pump that feeds the gas in the upperspace into high-pressure water and a dryer that dries said gas travelingupward in the high-pressure water, after said gas is collected andbefore it is released into the upper space.

(6) An apparatus for producing metallic particles as described in (4)above, wherein the apparatus has as an adjunct a water electrolyzer forproducing a mixture gas of oxygen and hydrogen.

(7) Metallic particles produced by the method described in (1), (2), (3)or (4) above or the apparatus described in (5) or (6) above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Flow chart of metal powder production as proposed by the presentinvention

FIG. 2: Schematic drawing of an apparatus for producing metal powder asproposed by the present invention

DESCRIPTION OF THE SYMBOLS

-   1: Apparatus for producing metal powder-   2: Pressure-resistant container for metal powder production-   3: Electrolyzer-   4: Mixture-gas injection pump-   5: High-pressure water tank-   6: Combustion chamber-   7: Pressure control valve-   8: Metal powder outlet-   9: Purified water-   10: Material element metal-   11: Ignition plug-   12: Metallic particles-   13: Metal feeder part-   14: Mixture-gas injector nozzle-   15: Hydrogen-gas feed pipe-   16: Oxygen-gas feed pipe-   17: Electrode-   18: Electrode-   19: Partition-   20: Water-   21: Atmosphere-gas suction pump-   22: Dryer-   23: Atmosphere-gas exhaust/circulation pump

BEST MODE FOR CARRYING OUT THE INVENTION

The following explains the present invention by taking a production oftitanium metal powder as an example. Note, however, that the inventionis not limited to production of titanium powder.

First, according to the present invention, purified water such asdistilled water and inert gas such as argon are filled into thehigh-pressure water tank, which is the pressure-resistant tank fortitanium-metal powder production, and the tank is pressurized at a highpressure. Then, material titanium metal such as a titanium bar is fedfrom the material element-metal feeder part, hydrogen and oxygen areinjected from the nozzle as a mixture gas, and this mixture gas isignited and completely burned inside the combustion chamber to achieve aperfect combustion state leaving an ultrahigh-temperature steam gas.Material titanium is instantly melted in this combustion gas anddispersed in water. Since the combustion atmosphere is inert gas, amajority of the produced titanium droplets remain as metal. Thus veryfine titanium particles of micron order are generated and dispersed inwater in powder form. The produced fine titanium powder precipitates ina short period.

Since the mixture gas of oxygen and hydrogen has a theoretical mixtureratio of 1 to 2, the gas bums completely even in an inert gas atmosphereto reach a maximum temperature of 2850° C. The resulting steam will befed into high-pressure water via an atmosphere-gas suction pump, wherethe steam is condensed and mixed with high-pressure water. The inert gascollected from water will be circulated back to the upper space of thehigh-pressure water tank after removing moisture content with a dryer.

The present invention can produce titanium powder of high purity at avery high efficiency. To achieve this, it is important to control theamounts of gases to be mixed and burned, reaction pressure and feed rateof material titanium metal.

With the production apparatus proposed by the present invention, anideal injection amount of mixture gas is approx. 3 to 5 liters persecond when the container can hold one ton of purified water. Applyingtoo high a gas pressure may damage the apparatus structure, while a lowpressure may cause the gas to flow upward from the nozzle, causing theheated, molten metallic particles to be encapsulated in air bubbles anddiffused from the water surface. This will reduce the generationefficiency of metallic particles. The water pressure in the pressuretank should be 5 to 10 atmospheres. An appropriate feed rate of materialtitanium metal into the combustion chamber is 0.3 to 0.5 kg/min.

The supplied material titanium metal should preferably have the highestpossible purity, in order to prevent impurities from mixing into theproduced titanium powder.

A mixture gas of hydrogen and oxygen provides the most efficient andstable means of melting titanium metal (melting point: 1660° C., boilingpoint: 3300° C.), where high pressure is required to ensure stablecombustion. Physical or chemical explanations as to why molten titaniummetal melts instantly and becomes fine particles in high-pressure waterhave not been found yet; however, it is considered that the moltendroplets are dispersed and broken into small pieces due to the impact ofcolliding with the water surface.

Material titanium metal may take a shape of bar, sheet, granule or foil,or any combination thereof, and it may be appropriate to supply granulesinstead of bar if the capacity of the production container is muchsmaller than one ton.

In addition to titanium, the material element metals that can be used inthe production of metal powder using the production apparatus proposedby the present invention include, but not limited to, zirconium (Zr),germanium (Ge), tin (Sn), gold (Au), platinum (Pt) and silver (Ag).

The high-pressure water tank used in the apparatus proposed by thepresent invention is a pressure-resistant tank made of metal, orpreferably steel, and ideally other parts such as the combustion chambershould also be made of steel. The gas pump is installed to blow out amixture gas at high pressure. Material element metal is fed continuouslyin accordance with the melt amount.

Material element metal must be fed into a position where the mixture gasburns completely and fully turns into a steam gas of ultrahightemperature. The combustion chamber is installed to burn the mixture gasto achieve this purpose. This setup allows for production of pure metalpowder free from impurities or byproducts. High pressure is alsorequired to completely bum a pure mixture gas.

An actual embodiment of the present invention is explained according tothe drawings. Note, however, that the invention is not limited to thisexample.

FIG. 1 shows a flow chart of metal powder production as proposed by thepresent invention, as described earlier. An apparatus for producingmetal powder (1) shown in FIG. 2 consists of a pressure-resistantcontainer (2) that comprises a high-pressure water tank (5), an injectornozzle for mixture gas of oxygen and hydrogen (14), a materialelement-metal feeder part (13), an ignition plug (11) and a combustionchamber (6).

The upper space of the container is filled with inert gas, and a pump(21) to deliver this atmosphere gas into high-pressure water, as well asanother pump (23) that exhausts and circulates into the upper space theinert gas collected from water and dehumidified through a dryer (22),are installed.

The apparatus for producing metal powder (1) consists of apressure-resistant container for metal powder production (2), and thepressure-resistant container for metal powder production comprises a gasinjection pump (4), a high-pressure water tank (5), a combustion chamber(6), a pressure control valve (7), a metal powder outlet (8), purifiedwater (9), material element metal for powder production (10), anignition plug (11), a material element-metal feeder part (13) and amixture-gas injector nozzle (14). (12) indicates produced metal powder.

Purified water (9) such as distilled water is filled into thehigh-pressure water tank (5) of the pressure-resistant container formetal powder production (2), and material titanium metal (10) such as atitanium metal bar is fed from the material element-metal feeder part(13), after which the container is pressurized at a high pressure.Hydrogen and oxygen are injected from the nozzle (14) as a mixture gasand the mixture gas is ignited by the ignition device (11). The mixturegas is completely burned in the combustion chamber (6) to obtain aperfect combustion state leaving an ultrahigh-temperature steam gas, andthe material titanium melts instantly in this combustion gas anddisperses in water.

At this time, very fine titanium particles of micron order (12) areproduced and dispersed in powder form. The titanium metal powder doesnot melt or float and precipitates as powder in a short period. Theseparated powder is then released from the outlet for titanium powder(8) and becomes titanium powder.

The supply of mixture gas of hydrogen and oxygen must be preciselycontrolled to achieve a hydrogen-to-oxygen ratio of 2 to 1. While amixture gas of hydrogen and oxygen is supplied from commercial gascylinders, adding a water electrolyzer (3) as an adjunct to produce amixture gas of hydrogen and oxygen via electrolysis of water willgenerate completely pure gases to facilitate an optimal, efficientsupply of mixture gas.

In the present invention, adding a water electrolyzer (3) as an adjunct,instead of supplying a mixture gas of hydrogen and oxygen fromcommercial gas cylinders, will generate completely pure gases viaelectrolysis of water, thereby facilitating a supply of mixture gas in asimple and efficient manner. When adding a water electrolyzer forproduction of mixture gas of oxygen and hydrogen as an adjunct, theelectrolyzer (3) is considered an optional adjunct unit to produce andsupply a mixture gas of hydrogen and oxygen via electrolysis of water,which consists of feed pipes for hydrogen and oxygen gases (15, 16),electrodes (17, 18), a partition (19) and water (20). The electrolyzercauses electrolysis of acid or alkali raw water to generate oxygen gasat the anode and hydrogen gas at the cathode, and supplies them as amaterial mixture gas.

Production Conditions and Results

Pressurized water: 1 ton Pressure: 2 kg/cm²(2 atmospheres)

Internal pressure of production tank: 2 atmospheres

Mixture gas: 5 L/sec (3.5 atmospheres)

Injection period: 1 hour

Feed rate of titanium metal: 30 kg

Production volume of titanium powder: Approx.30 kg

Evaluation of Produced Titanium Powder

The element titanium powder contained no byproducts or impurities andexhibited excellent uniformity of granular sphericity and consistency ofgranule size. The production cost was reduced around a half comparedwith the conventional technologies.

Industrial Field of Application

The present invention allows for production of high-purity metal,especially titanium powder, in a very efficient manner. The productionmethod proposed by the present invention achieves pure powder free frombyproducts or impurities other than the elemental component, wherein theproduced powder offers excellent uniformity of granular sphericity andsize and can be produced at significantly less cost. Batch production,continuous production and mass production are also possible.

1. A method for producing metallic particles, comprising: filling withinert gas an upper space of a high-pressure water tank containinghigh-pressure water, wherein a combustion chamber is formed in saidspace, said combustion chamber comprising an injector nozzle for mixturegas of oxygen and hydrogen, an ignition device, and a metal materialfeeder; igniting inside said combustion chamber via the ignition devicethe mixture gas of oxygen and hydrogen injected from the injectornozzle; applying the resultant combustion gas to melt or vaporize ametal material fed by the metal material feeder; and contacting theproduced molten metal droplets or vapor with high-pressure water tocrush and solidify the droplets/vapor to produce fine metallic particleswhich precipitate in water for recovery.
 2. The method for producingmetallic particles as described in claim 1, wherein the inert gas in theupper space of the high-pressure water tank is fed into thehigh-pressure water via a pump and said gas is collected as it travelsupward in the high-pressure water, dried, and then released into theupper space.
 3. The method as described in claim 2, wherein said metalmaterial is titanium, zirconium, germanium, tin, gold, platinum orsilver.
 4. The method as described in claim 2, wherein the shape of saidmetal material is bar, sheet, wire, foil or granule, or any combinationthereof.
 5. The method for producing metallic particles as described inclaim 1, wherein said metal material is titanium, zirconium, germanium,tin, gold, platinum or silver.
 6. The method as described in claim 5,wherein the shape of said metal material is bar, sheet, wire, foil orgranule, or any combination thereof.
 7. The method for producingmetallic particles as described in claim 1, wherein the shape of saidmetal material is bar, sheet, wire, foil or granule, or any combinationthereof.
 8. The method as described in claim 1, further electrolyzingwater to produce the mixture gas of oxygen and hydrogen beforeintroducing the mixture gas into the combustion chamber.